An illumination environment when an image is captured changes variously, for example, due to intensity of light from a light source such as sunlight and illumination and effects of a shield that shields light from the light source. When the illumination environment changes, a color of a subject in the image changes into various colors even though the subject is the same.
In this case, there arises a difference between the colors that the subject originally has and the colors of the subject in the captured image according to the illumination environment. Therefore, for example, a color chart in which patches are arranged is captured together with a subject, the patches being obtained by correctly measuring in advance colors by means of a colorimeter etc., and the colors of the subject are corrected with reference to the colors of the patches in the image. That is, for example, a corrected value is calculated so that the color of a patch in the image is made close to the correct color that the patch originally has. By correcting the color of the subject in the image by using the obtained corrected value, it is possible to reproduce the color that the subject originally has.
In the fields of health and beauty, an image of a skin surface is captured, and data on skin conditions, such as the skin color, the number and size of pores, and the size and color density of freckles is obtained from the image, and the skin condition is evaluated according to the data.
In this respect, a technique for improving color measurement accuracy is known. In addition, a technique is known for always calculating correct corrected data even when abnormal data is retrieved in imaging data because external light changes or imaging is interrupted by an obstacle when a test pattern is imaged. A technique is known for suppressing image degradation of a projected image without much labor and time. A technique is known for correcting a color tone deviation between two print pieces without using a color chart. A technique is known for correcting the color tone of an image output apparatus by suppressing unnecessary color-tone conversion. A technique is known for easily extracting an arrangement order of color chip-labeled areas. (For example, see Patent Documents 1-6.)
Patent Document 1: Japanese Laid-open Patent Publication No. 2013-195243
Patent Document 2: Japanese Laid-open Patent Publication No. 2005-150779
Patent Document 3: Japanese Laid-open Patent Publication No. 2001-134252
Patent Document 4: Japanese Laid-open Patent Publication No. 2013-110696
Patent Document 5: Japanese Laid-open Patent Publication No. 2013-26921
Patent Document 6: Japanese Laid-open Patent Publication No. 2013-196373